1. Field of the Invention
The present invention relates generally to a safety belt arrangement for a vehicle, such as an automotive vehicle. More specifically, the invention relates to a safety belt arrangement with a so-called pretensioner or preloader mechanism which is sensible of excessive deceleration energy or collision shock for instantly retracting extra length of belt.
2. Description of the Background Art
In general, safety belt arrangements are mounted on vehicles for safety of passengers on the vehicle upon occurrence of collision. Generally, such safety belt arrangements operate to retain passengers on their seat so as to prevent them from colliding onto installations in the vehicle cabin.
Conventionally known safety belt arrangements include belt spools in belt retractors, these belt spools are normally biased toward the retracting direction, and have a locking mechanism for locking the belt spool for preventing the latter from rotating in extracting directions in response to excessive vehicular deceleration and/or excessive belt extraction speed. However, such an emergency lock retractor type safety belt system cannot completely avoid the so-called film spool effect of permitting a short length of belt from the belt spool even after establishing locking.
To improve this, safety belt arrangements were proposed with a so-called pretensioner mechanism which is responsive to excessive deceleration energy upon collision and so forth, and takes action of the driving belt spool in the retracting direction for tightening the belts to ensure prevention of the passengers' movements. This prior proposed pretensioner mechanism comprises a cylinder with a piston disposed therein. The piston is connected to one end of a friction wire element which has the other end associated to a pulley secured on a axle of a belt spool. In case of emergency, the piston is driven by pressure generated by a gas generator for instantly driving the belt spool in the retracting direction via the pulley. Engagement between the pulley and the spool axle is established by means of gear engagement between an internal gear formed on the inner periphery of the pulley and a pinion gear rigidly secured on the spool axle, or by means of a kind of clutch mechanism which comprises a clutch member with an internal gear and a pinion gear secured on the spool axle.
In the case where the gear arrangement is employed, the pulley and the friction wire are normally placed away from each other and come into frictional engagement when the piston is driven. This construction causes lag time for driving the belt spool in the retracting direction. On the other hand, in the case where the clutch mechanism is employed, construction becomes complicated. Furthermore, by the instant load applied to the clutch mechanism, tendency of breakage is feared.